1. Technical Field
The present invention relates to a method and a system for localizing circular objects in video frames captured by an image capture unit, which can be applied, in particular, to pupil localization for eye surgery using excimer laser.
2. Description of Related Art
Excimer laser-assisted eye surgery is a common and effective procedure for treating visual impairments such as myopia, hyperopia, and astigmatism. During the procedure, however, the eye operated on may move unconsciously such that a positioning error of pupil center may occur. The error may keep the cornea in surgery from having the intended shape and thus compromise the result of the treatment. Such a positioning error of pupil center can be reduced by auxiliary eye stabilizer equipped with video-based, real-time eye tracker.
Locating the center of a pupil accurately in real time in the development of a video-based eye tracker is a challenging task. For example, several challenging problems may affect the tracking accuracies of pupil centers in video frames, including the following: referring to FIG. 1A, the detected edge of a pupil may be fragmented due to specular reflections of supportive light; referring to FIG. 1B, iris textures may hinder the tracker from determining the true edge boundary of a pupil; referring to FIG. 1C, uneven lighting conditions from the surrounding environment may degrade the accuracy of pupil circle estimation; and referring to FIG. 1D, a pupil image may be blur due to defocus, eye movements and/or surgical smokes.
While many eye detection and tracking techniques, such as those discussed in D. Hansen and Q. Ji, “In the eye of the beholder: A survey of models for eyes and gaze,” IEEE Trans. Pattern Analysis and Machine Intelligence, vol. 32, no. 3, pp. 478-500, 2010, have been developed for gaze detection and/or iris recognition, few of them are used in medical applications and report high localization accuracy in tracking pupil centers. Moreover, the challenging problems for video-based pupil localization, as shown in FIGS. 1A-1D, are rarely discussed in the related prior art.